In recent years, with the advancement of electronics technology and storage elements such as flash memory and the like in particular, small, high-storage capacity nonvolatile rewritable storage devices have been used in practical application. However, since these nonvolatile storage devices are primarily designed for general use so as to be usable in any personal computer or mobile device, personal information and other important information stored in the storage devices will be leaked to a third party in a case in which the storage devices are lost or stolen. Therefore, the information stored in the storage devices may be encrypted to thereby avoid the leakage of the information to a third party (e.g., see Patent Document 1).    Patent Document 1: Japanese Laid-open Patent Publication No. 2004-127183